I'm with Queen of Poop - couldn't they do a needle biopsy, just take a tiny sliver for pathology?

If she were my cat, I'd be done waiting. You've given the lump a chance to go away or grow. It's still there, and from what I am picking up from your posts - it's driving you nuts!! Right?

So find out what kind of tissue is there - then make an informed decision on how to proceed.